"We hadn't plotted six episodes. We had some vague ideas of where we'd go. So, it's not like we had to [change] the entire thing. It's about upping the scale of the threat. But without giving too much away, what we'd like to do if we get some more is tackle some of the favourite stuff. And what that would mean, if we could, would be to start then making it feel like our version. So, if anybody was to say you're doing Moriarty too quickly, it's really about not deferring your pleasures, you know? Why wait for season five?"